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Lecture 15

Astronomy Lecture 15.docx

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Patrick Mc Graw

Astronomy Lecture 15 - All terrestrial planets were formed in a similar way, but why did they all turn on out so differently? Brain storm the terrestrial planets - All the terrestrial planets are rocky, cratered, and differentiated - What are some differences amongst the terrestrial planets? - There atmospheres - Temperature variation - Length of orbital period - Lava (volcanic activity) - Water - Habitability -> life - Size / mass - Colour -> surface composition - Distances - Moons (or none) Terrestrial planet evolution - Recall that terrestrial planet formation begins with condensation and accretion - Each planet experience the next three steps to a different degree - 1. Differentiation - 2. Heavy bombardment - 3. Slow surface evolution - The earth will be our planet of reference. Differentiation: melting and separating - In order to differentiate, the Earth had to be heated by - Heat of formation (mechanical energy of accreted planetsimals – thermal energy) - Radioactive decay - Materials became separated into layers by density - Crust: low density rock, 10-60km deep – extremely thin - Mantle – denser solid rock that behaves like a slow Seismic measurements reveal the core - Different types of waves from earthquakes can be detected at different locations of the planet - P waves: are forward and backward (longitudinal) - S waves: are moving side to side - S waves cannot travel through liquids - Detecting p waves but not s waves indicated a liquid core - Multiple measurements of seismic waves from an earthquake can measure the size of the liquid one - P waves are refracted when density changes Heat flows from hot to cold - Core temp – 6000K; empty space – 3K - Energy is transported outward from the core to space in 3 ways - Hot material rises and cool material falls in convection cells - Conduction carries thermal energy through the coky crust - Radiation carries infrared energy from the surface to space Earth’s magnetic field - The existence of earth’s magnetic field means the core is partly liquid metal - A magnetic field helps to shield the earth from the harmful parts from the sun - They get trapped in the magnetic field The formation of the atmosphere - All terrestrial planets were equally imapacted during heavy bombar
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